1. Field
Exemplary embodiments of the present invention relate to a memory device, and more particularly, to a repair operation of a memory device.
2. Description of the Related Art
In the early stage of the semiconductor memory device industry, there were many original good dies, which means memory chips produced after going through a semiconductor fabrication process have no defective memory cells on the wafers. However, as the capacity of memory devices increases, it becomes difficult to fabricate a memory device that does not have any defective memory cells. That is, there is little possibility that a memory device can be fabricated without any defective memory cells.
To address this concern, a repair method of providing redundancy memory cells in a memory device and replacing defective memory cells with the redundancy memory cells has been proposed.
Generally, when a process of fabricating a wafer of a memory device is completed, a test is performed on the wafer to decide whether or not the memory cells operate normally. After the test, memory cells that are defective are replaced with repair memory cells in the wafer state through a repair operation. This is a normal repair operation that is performed in the wafer state. Differently from the normal repair operation, there is a Post-Package repair operation (PPR) which is a repair operation performed after the memory device is packaged. With the post-package repair operation, it is possible to repair defective memory cells that are not detected in the wafer state but are detected when a user uses the memory device after the memory device is packaged.
The post-package repair operation includes a hard post-package repair operation and a soft post-package repair operation. The hard post-package repair operation is a repair operation, the effect of which lasts permanently once the post-package repair operation is performed. The soft post-package repair operation is a temporary repair operation, the effect of which disappears when power is not supplied to the memory device. For example, when a hard post-package repair operation is performed to replace a particular memory cell X with a redundant memory cell Y, the memory cell X is permanently replaced with the redundant memory cell Y. However, when a soft post-package repair operation is performed to replace the memory cell X with the redundant memory cell Y, the repair operation for the memory cell X has to be repeatedly performed whenever power is newly supplied to the memory device.